Refrigeration plant suitable for air conditioning systems

ABSTRACT

A refrigeration system which is particularly suitable for air conditioning units for motor vehicles is disclosed. The system includes a compressor which is permanently connected to the engine of the vehicle and thus is running whenever the engine is running, a condenser, and an evaporator, the outlet of the evaporator being connected to the compressor via a control valve which is controlled by a barometric capsule sensitive to the pressure at the inlet of the compressor, and which closes so that the flow path therethrough is a minimum constricted orifice when the pressure at the inlet falls below a critical threshold value representing approach of the frosting temperature at the evaporator, to effectively stop the operation of the refrigeration system. The minimum flow during cut-off is required to ensure that the continuously rotating compressor is not damaged.

Peruglia June 25, 1974 REFRIGERATION PLANT SUITABLE FOR AIR CONDITIONING SYSTEMS [75] Inventor: Marco Peruglia, Turin, Italy [73] Assignee: Fiat Societa per Azioni, Turin, Italy [22] Filed: Mar. 12, 1973 [21] Appl. No.: 340,630

[30] Foreign Application Priority Data Apr. 19, 1972 Italy 68225/72 [52] U.S. Cl. 62/217 [5 l] lint. Cl. F25b 41/04 [58] Field of Search 62/196, 217, 323

[56] References Cited UNITED STATES PATENTS 2,766,593 l0/l956 Mitchell 62/2l7 3,688,517 9/1972 Newton 62/2l7 Primary Examiner-Meyer Perlin Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A refrigeration system which is particularly suitable for air conditioning units for motor vehicles is disclosed. The system includes a compressor which is permanently connected to the engine of the vehicle and thus is running whenever the engine is running, a condenser, and an evaporator, the outlet of the evaporator being connected to the compressor via a control valve which is controlled by a barometric capsule sensitive to the pressure at the inlet of the compressor, and which closes so that the flow path therethrough is a minimum constricted orifice when the pressure at the inlet falls below a critical threshold value representing approach of the frosting temperature at the evaporator, to effectively stop the operation of the refrigeration system. The minimum flow during cut-off is requiredto ensure that the continuously rotating compressor is not damaged.

1 Claim, 2 Drawing Figures REFRIGERATION PLANT SUITABLE FOR AIR CONDITIONING SYSTEMS BACKGROUND OF THE INVENTION The present invention relates to a refrigeration system and particularly to a system of the type having means for controlling operation to prevent frosting. This invention finds particular utility in connection with air conditioning systems for motor vehicles.

The compressor of air conditioning systems of this type is'usually driven by the engine of the vehicle via a coupling, such as an electromagnetic connector, which can be connected and disconnected by electrical control. In order to maintain the desired temperature of the evaporator of the system, and in particular to prevent the external temperature of the evaporator from reaching frosting point, which would result in the formation of frost in the interstices of the evaporator and thus obstruction of the passages of cooled air thereby reducing the efficiency of the system, a thermosensitive element is provided, this acts to disconnect the electromagnetic coupling when the sensed temperature approaches frosting point.

The necessity for the electromagnetic coupling and the thermosensitive element in the system leads to various disadvantages the most important of which are the cost of production and installation, the difficulty of calibrating the thermosensitive element, the susceptibility of the electromagnetic coupling to damage and difficulties due to the repeated sudden connection and disconnection of the coupling of the compressor. This latter disadvantage arises because the inertia of the compressor, and the power absorbed by the compressor even though small, are nevertheless appreciable relative to the power of the engine.

OBJECTS OF THE INVENTION It is one object of the present invention to overcome these disadvantages by providing means for controlling the minimum temperature of the evaporator by limitation of the delivery of the cooling fluid to a compressor which is permanently coupled to the engine, rather than by disconnection of the compressor as has hithertofore been the practice.

SUMMARY OF THE INVENTION According to the present invention, there is provided a refrigeration system comprising a compressor, a condenser fed by the compressor, an evaporator fed by the condenser through an expansive value and means connecting the output of the evaporator to the input of the compressor, in which the said means include a normally open valve assembly which is sensitive to the pressure at an inlet port thereof and which moves to a position allowing only a restricted flow therethrough when the pressure at the said inlet port falls below a predetermined threshold value corresponding to a temperature at the evaporator in the vicinity of the frosting point.

Onefeature of embodiments of this invention is that when the fluid has passed through the evaporator it is under saturated vapour conditions so that there is a direct relation between the temperature of the evaporator and the pressure of the fluid therein. By this means it is possible to use thepressure in the evaporator in order to control the temperature and operation of the BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of a cooling system according to this invention; and

FIG. 2 is a section of a valve assembly forming part of thesystem of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. I there is shown a compressor 10 of a conventional type which draws fluid, which may be, for instance, the fluid known under the trade name Freon 12, from an evaporator 12 through a conduit 14 via a control valve 200 and a conduit 16, and passes it under pressure along a conduit 18, and through a condenser 22 the output from which is connected to an evaporator 12 through an expansion valve 17 by a conduit 24. The valve 200 is also connected through a conduit 28 to a point 26 downstream of the compressor 10, the conduit 28 being connected to a control port 225 of the valve 200.

The control valve 200 comprises a body 202 in which there is a first horizontal (with reference to the orientation shown in FIG. 2) substantially cylindrical passageway 203 having an outlet port 201 connected to the compressor 10, and a second substantially cylindrical passageway 204 having an inlet port 206; the two passageways 203 and 204 communicate with one another through an opening 208 in a wall 205 the upper edge of which forms a valve seat 207.

The first passageway 203 is furnished with a radial aperture or orifice 208 near the outlet port 201, and this aperture communicates with a cylindrical chamber 210 the axis of which extends transverse the axis of the passageway 203. A shutter 211 is located in the chamber 210 and movable so that it can close the orifice 209 or can allow communication between the passage 203 and the chamber 210; a spring 212 is positioned to bias the shutter 211 to this latter position. The axial position of the shutter 211 and thus the opening and closing of the passage 203 is also affected by the pressure in the chamber of a barometric capsule, which may be of a known bellows type, within which there is a vacuum. The capsule is kept in normal position by an internal spring (not shown) and contracts when the ambient pressure, that is the pressure within the chamber 210, reaches a threshold value; the top of the barometric capsule is fixed to a plug 215 which tightlycloses the chamber 210.

The passageway 204 is provided with a radial passageway 216 which communicates with a cylindrical chamber 217 which is substantially parallel with the cylindrical chamber 210. The passageway 216 has a throttle constriction 216a and inside the chamber 217 there is a fixed diaphragm 218, adjacent the passageway 217, which separates the chamber 216 into two parts. A first weak spring 219 acting against the fixed diaphragm 218 forces a shutter 220, having a flexible sealing rim 221 of elastomeric material, against the valve seat 207: a plug 222 closes the top of the chamber 217 and is provided with an axial bore 223 in which a piston 224 is slidable. The axial position of the piston 224 depends upon the pressure exerted against the upper face 2240 which is applied through the control orifice 225 which, as mentioned above, is coupled by the conduit 28 to a port downstream of the compressor 10. At the same time the position of the piston is also affected by the force exerted on its lower face 224b by a compression spring 226 located between the said lower face 224b and the fixed diaphragm 218. The piston 224 is able to transmit its axial motion towards the shutter 220 through a stem 227 located at each end in recesses 228 and 229 in the piston 224 and in the shutter 220 respectively.

The chambers 210 and 217 communicate with one another through a conduit 230. The diameter of the throttle constriction 2160 in the passageway 216 is less than the diameter of the radial orifice 209 so that, in the event of opening of the latter the pressure in the chambers 210 and 217 will both be the same as the pressure in the passageway 203.

The spring 226 is calibrated to a value of pressure which depends on the values of the parameters of the system, but which in the embodiment described is about 19 atmospheres. When the pressure downstream of the compressor exceeds the value to which the spring 226 is calibrated the force exerted on the face 22411 of the piston 224 exceeds that exerted by the spring and the piston 224 moves toward the passageway 203 urging the stem 227 to press on the shutter 220, which is thus pressed firmly on the valve seat 207 closing off the free communication which previously existed between the inlet port 206 and the outlet port 201 and leaving only a restricted communication via the opening 208; this is provided so as to prevent the compressor from drawing any lubricating oil from its container. As soon as the valve shutter 220 closes the compressor 10 is substantially prevented from drawing in any fluid, and thus the pressure at its outlet drops allowing the piston 224 to rise under the action of the spring 226. The valve shutter 220 remains closed due to the pressure difference across it and due to the bias of the spring 219.

However, as the pressure at the evaporator 12 increases due to a rise in temperature, that increase of pressure is transmitted through the throttle 216a and the passageway 216 to the chamber 217, and from there passes through the passage 230 into the chamber 210: when the pressure in the chamber 10 increases to the threshold value of the barometric capsule 214, this may be, for example, 2 atmospheres, the barometric capsule contracts and, overcoming the action of the internal spring, allows the spring 212 to raise the shutter 21] thereby opening the orifice 209. Since the diameter of the orifice 209 is greater than that of the throttle 2160 in the passage 216, the pressure in the two chambers 210 and 217 falls due to the action of the compressor 10 which is operating continuously. The pressure difference across the shutter 220 thus urges this away from the valve seat 207 against the action of the spring 219, reopening free communication between the inlet port 206 and the outlet port 201. The compressor is thus brought back to full delivery conditions.

When the pressure in the chamber 210 drops below the calibration value of the barometric capsule, this again lengthens and forces the shutter 211 to close the orifice 209 and the pressure in the chamber 217 forces the shutter 220 to return to the valve seat 207 closing direct communication between the ports 206 and 201.

1 claim:

1. In a refrigeration system of the type comprising a compressor having an inlet and outlet, a condenser and means connecting the outlet of the compressor to the condenser, an evaporator and means including an expansion valve interconnecting the condenser and the evaporator, means which interconnect the evaporator and the inlet to the compressor and include valve means provided with a valve body, said valve body having an inlet port connected to said evaporator and an outlet port connected to said compressor, a valve seat located between said inlet port and said outlet port, first valve shutter means operatively located in relation to said valve seat means and movable between first and second positions to open and close communication through said valve seat between said inlet port and said outlet port, and means senstive to the pressure in said inlet port operating to control the position of said first valve shutter means in dependence on the pressure in said inlet port, the improvement wherein said pressure sensitive means comprise a control orifice communicating with said outlet port,

second valve shutter means movable to open or close said control orifice,

a barometric capsule connected to said second valve shutter means and located in a second chamber, said barometric capsule being sensitive to the surrounding pressure in said second chamber to open said second valve shutter means when said surrounding pressure increases above a predetermined threshold valve,

means connecting said second chamber to said first chamber, and

means including a restrictor throttle connecting said first chamber to said inlet port, said control orifice being larger than said restrictor throttle whereby opening of said control orifice causes a reduction in pressure in said first chamber and consequent opening of said first valve shutter means. 

1. In a refrigeration system of the type comprising a compressor having an inlet and outlet, a condenser and means connecting the outlet of the compressor to the condenser, an evaporator and means including an expansion valve interconnecting the condenser and the evaporator, means which interconnect the evaporator and the inlet to the compressor and include valve means provided with a valve body, said valve body having an inlet port connected to said evaporator and an outlet port connected to said compressor, a valve seat located between said inlet port and said outlet port, first valve shutter mEans operatively located in relation to said valve seat means and movable between first and second positions to open and close communication through said valve seat between said inlet port and said outlet port, and means senstive to the pressure in said inlet port operating to control the position of said first valve shutter means in dependence on the pressure in said inlet port, the improvement wherein said pressure sensitive means comprise a control orifice communicating with said outlet port, second valve shutter means movable to open or close said control orifice, a barometric capsule connected to said second valve shutter means and located in a second chamber, said barometric capsule being sensitive to the surrounding pressure in said second chamber to open said second valve shutter means when said surrounding pressure increases above a predetermined threshold valve, means connecting said second chamber to said first chamber, and means including a restrictor throttle connecting said first chamber to said inlet port, said control orifice being larger than said restrictor throttle whereby opening of said control orifice causes a reduction in pressure in said first chamber and consequent opening of said first valve shutter means. 